The 256mg & 1 GB SC Cards are Scan Disk & the 8gb is HP. (I tried more than one size card just in case that was the problem but it is not.)
Yes, I have used the
https://www.sdcard.org/downloads/formatter_3/ and used the full overwrite mode.
No, the cards are NOT locked.
I have erased all books and reformatted cards more than once, putting just 1 ePub book on a card that I know can be opened on the reader, if put directly on to the reader.